PU Injection Process: Ultimate Analysis & Defect Elimination Guide
Figure1: PU injection core forming principle schematic
1 Three Core Physical Control Principles & Standard Parameters
All PU foaming defects derive from out-of-limit process parameters, three quantified industry execution standards as below:
- Metering & Mixing Control: A/B component allowable deviation ≤±0.5%; open-loop gear pump under 8h continuous production normally generates 2.5%~3.2% ratio drift, leading to hardness deviation over 7 Shore A; mixing head speed ≥3500rpm to reach ≥99% mixing uniformity, insufficient shear causes enclosed air bubbles.
- Temperature Control: Polyol 52~58℃, Isocyanate 58~64℃, ambient workshop fluctuation controlled within ±2℃; single 2℃ temperature shift changes raw viscosity by 18%+, trigger inconsistent cream time and uneven foaming; whole pipeline heat preservation required to avoid local cold spot.
- Injection Flow & Laminar Control: Adopt segmented dynamic injection curve, initial high flow for cavity filling, mid/late low-speed laminar advancing; flow velocity over rated value creates turbulent flow and entrapped air, too slow leads short-shot underfilling.
Common hidden risks from out-of-spec parameters: Ordinary open-loop gear pump under long-time production, ratio error usually reaches 2%~4%, scrap rate stays at 8.2%~15.7%.
2 Three Practical Factory Renovation Cases
Case1 High-Density Memory Mattress Factory
Annual Output 450,000pcs, original open-loop gear pump equipment.
- Original Trouble: Daytime temperature rise leads 3% ratio drift, batch hardness difference up to 9.2 Shore A, reject rate 12.8%.
- Upgrade Plan: Servo closed-loop + Coriolis mass flowmeter + high-shear mixing head.
- Post-data: Ratio tolerance ≤0.43%, batch hardness ≤1.7 Shore A, scrap down to 0.69%.
Figure2: Mattress collapse from ratio drift defect
Case2 150mm+ Cold Chain PU Sandwich Panel
Large refrigeration equipment manufacturer.
- Original Trouble: Raw temp fluctuation ±3.5℃, panel density gap 35kg/m³, warpage reject 8.7%.
- Solution: Three-layer jacket tank + full insulated hose + PLC line speed linkage.
- Post-effect: Density fluctuation ≤3.6kg/m³, reject down to 0.52%.
Figure3: Qualified cold storage sandwich panel
Case3 Auto NVH Complex Cavity Damper
Auto precision component producer.
- Original Trouble: Fixed injection speed causes air trapping rate 10.3%.
- Improvement: PLC three-stage variable flow injection programming.
- Post-data: Internal bubble fully eliminated, pass rate 89.7%→99.5%.
Figure4: Finished automotive NVH damping component
3 Industry-Based Equipment Selection Matrix
| Application Field | Core Product | Key Technical Requirement | Recommended Equipment Configuration |
|---|---|---|---|
| Cold Chain Construction | Insulation board, pipe shell | High continuous flow stability, ≥90% closed-cell rate | High-pressure multi-component machine + synchronous conveying line + full constant temp system |
| Furniture & Bedding | Memory foam, high resilience mattress | Low-flow anti-drift, fast formula switching | Servo closed-loop metering + Coriolis flowmeter + high-shear mixing head |
| Auto Parts | NVH damper, integral skin parts | Gram-level precision, dynamic flow + MES docking | Ultra-precision servo injection unit |
4 Frequently Asked Practical Questions
Q1 Can partial refit replace full machine replacement?
Q2 Suitable production workshop humidity?
Q3 Meter calibration cycle?
Conclusion
Eliminating mass-production foaming defects relies on systematic closed-loop control rather than raw material formula adjustment alone. Haifeng supplies customized process debugging and turnkey production solution according to actual workshop and product parameters.
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